Color kinescope with improved x-ray protection

ABSTRACT

The glass envelope for a kinescope for color television includes a faceplate panel with a peripheral flange for sealing with a funnel which defines a constricted neck portion. A shadow mask mounted within the peripheral flange of the faceplate panel is coated with a thin layer of bismuth. The constricted neck of the tube is encompassed with paper pulp impregnated with bismuth trioxide; and the external surface of the funnel from the paper pulp to the flange of the faceplate panel is coated with a nonconducting mixture of bismuth trioxide and sodium silicate thereby providing a kinescope with greatly improved X-ray protection.

United States Patent a corporation of Illinois COLOR KINESCOPE WITH IMPROVED X-RAY PROTECTION 9 Claims, 2 Drawing Figs.

US. Cl 313/85, 313/64; 117/335 Int. Cl H01j 31/20 Field of Search l l7/33.5A,

H 13,562,s1s

[56] References Cited UNITED STATES PATENTS 2,291,406 7 1942 Paehr 313/64 3,443,138 5/1969 Schwartz 313/64 Primary ExaminerAlfred L. Leavitt Assistant ExaminerWayne F. Cyron Attorney-Dawson, Tilton, Fallon & Lungmus ABSTRACT: The glass envelope for a kinescope for color television includes a faceplate panel with a peripheral flange for sealing with a funnel which defines a constricted neck portion. A shadow mask mounted within the peripheral flange of the faceplate panel is coated with a thin layer of bismuth. The constricted neck of the tube is encompassed with paper pulp impregnated with bismuth trioxide; and the external surface of the funnel from the paper pulp to the flange of the faceplate panel is coated with a nonconducting mixture of bismuth trioxide and sodium silicate thereby providing a kinescope with greatly improved X-ray protection.

COLOR KINESCOPE WITII IMPROVED X-RAY PROTECTION BACKGROUND The present invention relates to a color kinescope; and more particularly, it relates to a color kinescope with minimal X-ray penetration.

Ordinarily, the electron beams which scan the viewing area in a color television kinescope are energized by an accelerating potential of 25,000 volts. At this limit of accelerating potential, there is little or no danger of generating harmful X- rays. Further, since the faceplate panel of conventional color kinescopes are usually quite thicker thanthe rest of the tube and comprise a lead type of glass, whatever X-rays are generated within the tube are absorbed in the faceplate panel.

However, if the accelerating voltages exceed by as little as 2,000 volts the 25,000 volt specified accelerating potential, the safety limit for X-ray generation may be exceeded with -resulting hazardous generation and escape of X-rays. At this level, the X-ray penetration at the back of the tube becomes considerable, and additional protection must be provided.

In prior attempts to secure greater protection against X-ray penetration of cathode ray tubes, a system was suggested in SUMMARY The present invention provides for coating the shadow mask mounted within the peripheral flange of the faceplate panel of a conventional color kinescope with a thin layer of bismuth thereby substantially reducing the penetration of X-rays generated by high energy electron beams impinging on the phosphor screen escaping through the rear of the tube. In addition, the constricted neck portion of the tube is encompassed with a paper pulp sleeve impregnated with bismuth trioxide; and the external surface of the funnel from the paper pulp sleeve to the flange of the faceplate panel is coated with a nonconducting mixture of bismuth trioxide and sodium silicate. It has been found with this particular arrangement of tion 17 contains the electron beam generating means, commonly referred to as the electron gun, and generally designated I8 in the drawing. The final grid of each of the three separate guns (which is designated 19 in the drawing) is the accelerating grid which imparts the high energy to the electron beam emanating from the gun. A main deflection yoke is schematically illustrated at 20, and it is located at the base of the constricted neck portion 17 of the tube envelope for controllingthe deflection of the beam as it scans its raster.

As is known, the interior surface of the funnel I6 is coated with a graphite solution 21 to provide an electrically conducting shield completely covering the funnel from its juncture with the faceplate panel into the constricted neck portion adjacent the electron guns. The "dag," as it is commonly called, coating 21 is maintained at the high potential of the final accelerating grid, i.e. 25,000 volts.

The sources of X-rays generated within the tube include phosphor and aluminum coatings I2 and I3 on the interior of the faceplate panel as the electron beams impinge on them, and the shadow mask which absorbs'84 percent of the total current generated by the scanning electron guns.

In order to minimize penetration of X-rays through the rear of the tube, the present invention contemplates coating one surface of the shadow mask 14 with a thin layer of bismuth, identified by reference numeral 22 in the drawing. Although the bismuth coating 22 on the shadow mask 14 is shown as having been applied to the rear surface of the shadow mask means for protecting against X-ray penetration, there is provided sufi'rcient safety for personnel even if the accelerating potential rises to the 30,000 volt level.

Other features and advantages of the instant invention will be obvious to persons skilled in the art from the following detailed description of preferred embodiments accompanied by the attached drawing.

THE DRAWING FIG. 1 is a vertical cross section of a color television kinescope incorporating features of the present invention; and

FIG. 2 is a vertical cross section of a color television tube comprising an alternate embodiment of the present invention.

DETAILED DESCRIPTION Referring first to FIG. 1, there is seen a conventional color kinescope having a faceplate panel 10 with an integral peripheral flange II. On the interior of the faceplate panel 10 there is deposited a mosaic pattern of phosphor dots schematically designated by reference numeral 12. A thin coating of aluminum 13 covers the phosphor screen 12.

Mounted within the peripheral flange 11 is a shadow mask 14 which defines a plurality of apertures as at 15.

Fastened to the peripheral flange ll of the face plate panel 10 is a funnel 16 which defines a constricted neck portion 17 remote from the phosphor screen. The constricted neck por- 14, it will be appreciated that it could equally as well be applied to the front or convex surface of the shadow mask. A coating of bismuth having a thickness of Y5 mils has been found to offer a 200 percent safety factor at an electron accelerating potential of 30 kv. This is much beyond anticipated safety margins. Further, the present invention contemplates ensleeving or encompassing the constricted neck portion 17 with a paper pulp sleeve 23 which is impregnated with bismuth trioxide. The sleeve 23 substantiallyv covers the constricted neck portion of the gun and defines a flared portion 230 which begins to encompass the funnel. However, the major portion of the funnel is coated with a solution of bismuth trioxide and sodium silicate 24 for promoting the absorption of X-rays.

The thickness of the coating 24 is again of the order of 5 mils, and it may either be applied directly or applied in solution and baked on. The maximum thickness of this sodium silicate coating is 30 mils. After spraying the solution on the exterior of the funnel, it may then be baked on at the same time the dag is baked onto the interior of the funnel. The bismuth trioxide need not be applied in solution with the sodium silicate, and it can be mixed in an epoxy resin solution or other lacquer or other suitable vehicle and applied to the exterior of the funnel.

It has been found that a coating of bismuth trioxide of only I mil thickness (Le. 1 gram per 50 sq. centimeters) provides the same protection as a glass envelope of mils thick. This reduces the X-ray penetration of glass sleeves by a factor of 8:1.

Turning now to FIG. 2, an alternative embodiment is shown wherein the bismuth trioxide and sodium silicate coating is designated 24' and it is applied on the interior of the funnel as a separate, nonconducting coating covering the dag solution. It will be noted that in order to accomplish this, two separate steps are required, and therefore, the previous embodiment is preferred. However, the bismuth trioxide and sodium silicate coating can easily be baked on the inside of the funnel. Further, instead of the bismuth trioxide-impregnated paper pulp sleeve, as described in the earlier embodiment, the embodiment shown in FIG. 2 has an adhesive tape applied to the constricted neck portion of the tube generally covering the same area as the previous paper pulp sleeve, and in this case, the tape is designated by reference numeral 25 and it is also impregnated with bismuth trioxide.

Having thus described a preferred embodiment together with an alternative embodiment of my invention, it will be obvious that certain modifications and substitutions or equivalents may be made without departing from the inventive principle; and it is therefore, intended that all such modifications and equivalents be covered as they are embraced within the spirit and scope of the appended claims.

We claim:

1. In a color television kinescope having a glass faceplate panel, a funnel connected to said faceplate panel and defining a constricted neck portion, a shadow mask mounted within said faceplate panel and means for generating electron beams impinging on a phosphor screen deposited on said faceplate panel, the improvement comprising: a covering of a nonelectrically conducting solution consisting in substantial part of bismuth trioxide on the exterior surface of said funnel covering substantially all of said kinescopes exclusive of said faceplate panel; and covering means impregnated with bismuth engaging and covering said constricted neck portion.

2. The structure of claim 1 wherein said covering means is a paper pulp sleeve impregnated with bismuth trioxide for encompassing the constricted neck portion of said tube and adjacent to said external coating on said funnel.

3. The structure of claim 2 wherein said covering is about 5 mils thick.

4. The structure of claim 3 wherein said exterior coating on said funnel comprises bismuth trioxide and sodium silicate baked on said tube to provide a nonconducting exterior covering. 1

5. The structure of claim 1 wherein said covering means is an adhesive tape impregnated with bismuth trioxide wrapped around the constricted neck portion of said tube.

6. The structure of claim 1 further comprising a coating of conducting bismuth on said shadow mask.

7. The structure of claim 6 wherein said bismuth coating is about 5 mils thick.

8. in a color television kinescope having a glass faceplate panel, a funnel connected to said faceplate panel and defining a constricted neck portion, a film of conductive graphite on the interior of said funnel, a shadow mask mounted within said faceplate panel and means for generating electron beams impinging on a phosphor screen deposited on said faceplate panel, the improvement comprising: a nonelectrically conducting coating of bismuth trioxide and sodium silicate on the interior of said tube covering said graphite film and extending from the juncture of said faceplate panel and said funnel substantially into the constricted neck portion of said tube; and a coating of bismuth of at least about l mil thickness on said shadow mask.

9. The structure of claim 8 further comprising covering means impregnated with bismuth trioxide for engaging and covering the external portion of said constricted neck. 

2. The structure of claim 1 wherein said covering means is a paper pulp sleeve impregnated with bismuth trioxide for encompassing the constricted neck portion of said tube and adjacent to said external coating on said funnel.
 3. The structure of claim 2 wherein said covering is about 5 mils thick.
 4. The structure of claim 3 wherein said exterior coating on said funnel comprises bismuth trioxide and sodium silicate baked on said tube to provide a nonconducting exterior covering.
 5. The structure of claim 1 wherein said covering means is an adhesive tape impregnated with bismuth trioxide wrapped around the constricted neck portion of said tube.
 6. The structure of claim 1 further comprising a coating of conducting bismuth on said shadow mask.
 7. The structure of claim 6 wherein said bismuth coating is about 5 mils thick.
 8. In a color television kinescope having a glass faceplate panel, a funnel connected to said faceplate panel and defining a constricted neck portion, a film of conductive graphite on the interior of said funnel, a shadow mask mounted within said faceplate panel and means for generating electron beams impinging on a phosphor screen deposited on said faceplate panel, the improvement comprising: a nonelectrically conducting coating of bismuth trioxide and sodium silicate on the interior of said tube covering said graphite film and extending from the juncture of said faceplate panel and said funnel substantially into the constricted neck portion of said tube; and a coating of bismuth of at least about 1 mil thickness on said shadow mask.
 9. The structure of claim 8 further comprising covering means impregnated with bismuth trioxide for engaging and covering the external portion of said constricted neck. 